The present invention relates to a disk drive such as a compact disk, and more particularly, to a disk calibration and search method for a compact disk read only memory (i.e., a CD-ROM) disk drive, for increasing the setting accuracy of the number of disk tracks when a pickup searches the disk tracks in the disk drive.
As currently manufactured in commercial quantities, a compact disk is a small disk with, for example, a twelve centimeter outer diameter, on which a plurality of concentric or spiral tracks are formed along one side of the disk. These tracks comprise a multitude of fine grooves whose size corresponds to several micrometers are formed, and represent predetermined digitalized signals such as audio information signals and computer information signals. Each groove is called a pit and the space between the pits are called islands or lands. Generally, the tracks are spirally arranged from the center of the disk and the interval between the tracks is known as a pitch, and this interval or pitch is generally 1.6 μm.
When driving a sled motor for transferring a pickup of the compact disk drive radially across the disk, the rotation of the sled motor is controlled using a general frequency generator with a predetermined number of tracks in the disk corresponding to a single pulse generated from the frequency generator. For example, if a compact disk drive is designed such that a constant number of track zero crossing signals are always generated on the basis of a single rotation of the disk, due to manufacturing tolerances encountered during commercial production of the disk, the width of the pitch formed on the disk may vary between 1.4 μm to 1.8 μm, which are smaller and greater than the preferred standard pitch of 1.6 μm, respectively. That is, since the width of the pitch is not uniform, a different number of track zero crossing signals is generated for each disk. In addition, the difference in pitch causes an error in calculations performed during a track searching operation.
Therefore, in order to solve the above problem relating to the error in the above mentioned calculation, conventional compact disk drives adopt a method in which a program area of the disk is divided into twenty-four pages and the search is performed from a current page to an arbitrary page different from the current page, and then a searching error detected from the search process is reflected in the current page to update data of the current page. According to the conventional method, sufficient data updating should be achieved with respect to each current page so as to secure the ensuing correct search. Also, due to the deviation generated when the pickup searches the tracks from the inner circumference to the outer circumference of the disk, or from the outer circumference to the inner circumference of the disk, a microcomputer inner memory of 24(pages)×2×2 bytes is used, which I have discovered causes a lower efficiency in usage of the memory. Also, I have found that when the borders of the twenty-four pages of the disk are searched, the result obtained by calculating the track number is not particularly reliable. In addition, I have observed that when measuring the access time in the initial driving state of a compact disk drive, the track number is set on the basis of a test performance of only 100 to 500 access time measurements. Accordingly, since contemporary compact disk drives are not sufficiently stable, accuracy of the track search by the pickup is lowered.